Throughout the world, various communication regulatory bodies allow wireless communications devices, such as 802.11 devices, to operate in certain frequency bands subordinate to other transmitters. For example, in the United States unlicensed wireless devices are allowed to operate in the 5.250-5.350 and 5.470-5.725 GHz bands, provided that the devices employ dynamic frequency selection (DFS) to vacate the band if a radar signal is present in the band. Prior to and during transmission in these bands, the wireless device must monitor for radar waveforms and either vacate the band or flag the band as unavailable for present use by the device.
One such radar that the devices need to detect is bin-5 radar. Bin-5 radar waveforms are somewhat different from more traditional radar waveforms in that the bin-5 waveform is of very long duration and has a sparse energy distribution relative to more traditional radar waveforms, which may have durations on the order of hundreds of milliseconds. For example, the bin-5 waveform has a twelve second transmission period in which there may be very few pulses. In particular, a bin-5 waveform may have a total of 8 to 20 pulse bursts within the twelve second period. Each burst may have as few as one to three pulses.
The bin-5 waveform has several parameters whose values may be randomly selected, thus further complicating waveform detection. First, the number of pulses per burst may be randomly chosen. For example, there may be anywhere from one to three pulses per burst. Next, the space between pulses in a burst may be randomly chosen. For example, the inter-pulse arrival time could vary from between 1 ms and 2 ms. Furthermore, the length of each pulse in a burst has the same randomly chosen length between 50 to 100 microseconds. Finally, the time separation between each burst may be random. When these random factors, as well as others, are combined it is very difficult to recognize a pattern that corresponds to a bin-5 radar signal.
Due to the characteristics of bin-5 radar, techniques that are used to detect more traditional radars will either not work well or will be prohibitively expensive to implement if a bin-5 radar is to be detected. Note that if the device is not able to detect a radar with sufficient reliability, the device will not be qualified to operate in certain frequency bands.
While bin-5 is used as an example of a radar waveform whose detection is difficult, other waveforms of long duration and/or sparse energy distribution also present detection problems.
The approaches described in this section are approaches that could be pursued, but not necessarily approaches that have been previously conceived or pursued. Therefore, unless otherwise indicated, it should not be assumed that any of the approaches described in this section qualify as prior art merely by virtue of their inclusion in this section.